1. Field of the Invention
The present invention relates to a reversible ratcheting tool having a smaller head and improved driving torque for convenient use in a limited space.
2. Description of the Related Art
A wide variety of ratcheting tools have heretofore been disclosed. Typical examples include: U.S. Pat. No. 1,957,462 to Kress issued on May 8, 1934; U.S. Pat. No. 4,328,720 to Shiel issued on May 11, 1982; U.S. Pat. No. 5,626,062 to Colvin issued on May 6, 1997; U.S. Pat. No. 4,762,033 to Chow issued on Aug. 9, 1988; U.S. Pat. No. 4,520,697 to Moetteli issued on Jun. 4, 1985; U.S. Pat. No. 3,337,014 to Sandrick issued on Aug. 22, 1967; and U.S. Pat. No. 5,144,869 to Chow issued on Sep. 8, 1992. Most of the above-mentioned conventional ratcheting tools fail to provide high torque operation, as the pawls merely engage with the ratchet wheel by at best three or five teeth. The head of the ratcheting tool has to be relatively large for accommodating those components and thus is difficult to be used in a limited space. In addition, the pawl is directly driven by the switch button or reverser plate or like element such that the pawl tends to be disengaged from the ratchet wheel or like element if the switch block is inadvertently impinged. Generally, a skilled user uses a combination wrench, a spanner with two open ends, or a ring spanner for tightening or loosening a fastener in a limited space. Yet, it is found that free rotation of the ratcheting tool during ratcheting is too large (larger than the theoretic value of 5°), as the pawl has a long travel.
U.S. Pat. No. 6,431,031 issued on Aug. 13, 2002 discloses a reversible ratcheting tool with a smaller head to solve the above problems.
FIG. 8 illustrates engagement between a gear wheel 80 and a pawl 81 of a conventional ratcheting tool. The pawl 81 has a plurality of teeth engaged with teeth 83 of the gear wheel 80 at faces 82 so as to provide high torque operation. The faces 82 have a center of curvature at “B”, which is coincident with the center of the gear wheel 80. Referring to FIG. 9, when the handle (not shown) is rotated clockwise, the gear wheel 80 exerts a force F on each tooth on the pawl 81. The force F is imparted into a downward vertical force F1 and a leftward horizontal force F2. The leftward horizontal force F2 makes the pawl 81 bear against point A on a wall in a cavity in a web area of the handle. The downward vertical force F1 moves the pawl 81 away from the gear wheel 80. As a result, the right portion of the pawl 81 is disengaged from the gear wheel 80. The reactive force by the wall at point A is imparted into an upward vertical force FN1 and a rightward horizontal force FN2. The upward vertical force FN1 makes the pawl 81 move toward the gear wheel 80 and the rightward horizontal force FN2 moves the pawl 81 rightward. As a result, the pawl 81 and the gear wheel 80 have a firm engagement with each associated tooth of the gear wheel at point D.
Referring to FIG. 10, when the handle is further rotated clockwise, a higher torque is applied such that the magnitudes of the forces F1 and F2 increase. The right portion of the pawl teeth that is slightly disengaged from the gear wheel teeth 83 can still be in contact with the gear wheel teeth 83 when the gear wheel 80 is rotated. The right portion of the pawl 81 is moved downward farther. As a result, more teeth on the pawl 81 are disengaged from the gear wheel 80 (see the pawl teeth on the right side of point A). The forces FN1 and FN2 are also increased in magnitude, yet fewer pawl teeth have firm engagement with the gear wheel teeth. This problem is aggravated when the handle is further rotated clockwise. Accordingly, the gear wheel/pawl arrangement fails to provide the required high torque operation, as all of the pawl teeth have the same center of curvature. In addition, the pawl and the gear wheel will be damaged quickly.
The present invention is intended to provide an improved design in this regard to improve the driving torque for reliable high-torque operation.